Propagation of plants



Patented sep:. 6,'193s UNITED. STATES "PATENT morass-non or PLANTS Percy W. Zimmerman and Albert E. Hitchcock, Yonkers, N. Y., assignors to Boyce Thompson Institute for Plant Research, Inc., Yonkers, N. Y., a corporation of New York No Drawing. Application March 17, 1937, Serial No. 131,370

10 Claims. (Cl. 47-58) This invention relates to the propagation of plants from cuttings, and has for its object the provision of an improved method for inducing root-growth on such cuttings. This application is a continuation in part of our copending ap plication Serial No. 72,058, filed April 1, 1936.

It has heretofore been recognized that certain gases (e. g. ethylene) induce definite types of formative responses on plants, such as stimulation or retardation of the growth of certain tissues, and the initiation of cell division which results in various kinds of proliferations or in the formation of roots. As a result of an exhaustive investigation of the effects of various types of growth substances on plants, we have discovered that certain organic compounds exercise a pronounced stimulating effect on rootgrowth, and are highly valuable in promoting and inducing root-growth on'plant slips or cuttings, In this specification and in the appended claims, the word cutting and the expression cuttings and the like are usedgenerically to designate any part of-a plant, including buds, scions, and slips, used for purposes of propagation, and the invention advantageously may be employed to promote plant propagation from any such plant part by inducing active callus formation, rootgrowth, and similar plant physiological responses.

Among the organic compounds which we find useful for inducing root-growth are indolepropicnic acid and its derivatives. In the appended claims these compounds are defined generically as indole substitution products of a compound having the propionic acid structure as its nucleus, that is, the propionic acid structure (which does not include the acid hydrogen atom of propionic acid itself) is the base or foundation of the molecule of the compound.

Based on the foregoing discovery, our present invention involves the improvement in propagating plants from cuttings which comprises the step of inducing root-growth by subjecting the cutting to the action of a substance of the group consisting of indolepropionic acid and its derivatives. Only a minute amount of the substance is necessary to induce vigorous rootgrowth and high concentrations are usually in- Among the derivatives of indolepropionic propionic acid and esters of indolepropionic acid. The alkali metal salts (including the ammonium salt) and the alkali-earth metal salts of indolepropionic acid in general are the preferred salts for use in carrying out the invention. The lower alcohol esters (such as the methyl and ethyl esters) of indolepropionic acid constitute the preferred esters for use in carrying out the invention. So far as we have now determined, however, all of the salts and esters of indolepropionic acid possess definite powers of inducing rootgrowth and similar plant physiological responses on cuttings and the like.

Treatment of the more succulent type of plants, such as the tomato, African marigold, tobacco, etc., with the growth substances of the present invention (1. e. indolepropionic acid and its derivatives) has shown that roots may be induced to grow from any portion of the stem, and even from the leaves of many species. The growth substance may be mixed with lanolin, olive oil, paraffin oil, maize oil, castor oil, Amalie" oil (a commercial mineral oil) and the like, and a thin film of the mixture may be applied by rubbing 'with a glass rod on the epidermis of the-region to be treated. The usual concentrations found most eilective are from about 0.01 to 2% of the growth substance on the weight of lanolin or the like. Lanolin and similar preparations of the growth substance may be applied directly to the cutting, 'or they may be placed on shoots which remain attached to the parent plant during the period of treatment and are then removed and made into cuttings that are handled at this stage the same as is normally done in commercial practice. When applied to the stems, the growth substances of the present invention definitely cause local initiation of roots on growing plants of tomato, sun flower, marigold, artichoke, buckwheat, dahlia, and tobacco. If the plants are kept in a, glass case after treatment, the new roots force their way through the epidermis and out into the humid atmosphere. The time required for roots to make their appearance varies with the growth substance used, the concentration,the species of plants, and the exact place on the plant where the material is applied.

Indolepropionic acid itself is especially efiective for initiating roots on both stems andleaves. In the case of indolepropionic acid itself, a 0.01 to 2.0% solution in lanolin causes negative (away from side where substance was applied) bending of tomato stems. Positive (toward side where substance is applied) bending occurs when the concentration of the substance is high enough to injure the tissue or retard the normal rate of growth. A 0.1 to 2.0% solution of indolepropionic acid in general is optimum for inducing adventitious roots.

In general, it might be stated that the most effective concentration for root initiation falls just below that causing positive bending of the stem, or at the point where there is slight retardation of growth. When the concentration is high enough to cause evident injury, roots appear on the opposite side or adjoining the place on the stem where the substance is applied. This result indicates that as the growth substance diifuses away from the point of toxic concentration a range is reached which is eifective for inducing roots. Under favorable conditions, 10 to 20 mg. of indolepropionic acid per gram of lanolin causes roots to be induced and appear through the epidermis on tomato in six days, marigold in five days, tobacco in eight days, and artichoke in six days. Two milligrams of indolepropionic acid per gram of lanolin are efiective, but usually require about two days more to induce roots.

In commercial practice, treatment of the cutting or parent plant with a water solution of the growth substance is generally more satisfactory and applicable than treatment with lanolin (and similar) preparations. Thus, the growth substance may be dissolved in the water (in which it is only sparingly soluble), and the basal end of the plant cutting placed in the solution. The basal end of the cutting immersed in such a solution for from several hours to several days induces subsequent growth of excellent root systems. The concentration of the growth substance in the aqueous solution is relatively minute, say a few milligrams per 100 cc. of water. Thus, solutions containing 2 to 20 mg. of indolepropionic acid per 100 cc. of water give satisfactory results for many species.

In practicing the invention with water solutions of the growth substances, the plant cutting is placed in the solution for a period of time ranging from a few hours to several days. The cutting, after treatment in the solution, may be planted in a mixture of half sand and half peat moss, for example, or in soil. The effectiveness of the treatment is indicated in many ways, such as the increased percentage of rooted cuttings, increase in size of the root systems, earlier appearance of roots, greater total number of roots, and the emergence of roots from stem tissue above the base of the cutting as well as at the base.

Cuttings of American holly (Ilea: opaca) placed in solutions of indolepropionic acid (2 to 8 mg. per 100 cc.) for periods ranging from eight hours to two days produced excellent root systems six to ten weeks after treatment and planting. These results are of spcial significance since cuttings of American holly are difficult to root. A similar favorable response to treatment with water solutions of indolepropionic acid was obtained with Japanese maple at the end of six to ten weeks, Japanese holly (Ilem crenata) at the end of about four weeks, Taxus at the end of eight to ten weeks, American elm at the end of four to six weeks, and with many other genera and species at the end of periods ranging from two to ten weeks.

By the term "indolepropionic acid" as used herein and in the appended claims we refer specifically to beta-indolepropionic acid (beta- [indo1y1-(3) ]-propionic acid) having the structural formula ,CHzCHaC O OH The derivatives of indolepropionic acid referred to herein and in the appended claims are those compounds in which an atom other than a hydrogen atom or a radical has been substituted for the acid hydrogen atom of the indolepropionic acid particularly identified above.

We claim:

1. The improvement in propagating plants from cuttings and the like which comprises the step of inducing root-growth by subjecting the cutting to the action of an indole substitution product of a compound having the propionic acid structure as its nucleus.

2. The improvement in propagating plants from cuttings and the like which comprises the step of inducing root-growth on the cutting by applying indolepropionic acid directly tothe region at which it is desired to induce root-growth.

3. The improvement in propagating plants which comprises the step of inducing root-growth by subjecting the cutting to the action of an alkali metal salt of indolepropionic acid.

4.. The improvement in propagating plants from cuttings and the like which comprises the step of inducing root-growth by subjecting the cutting to the action of a lower alcohol ester of indolepropionic acid.

5. The improvement in propagating plants from cuttings and the like which comprises, the step of inducing root-growth on the cutting by applying a substance of the group'consisting of indolepropionic acid, salts of indolepropionic acid, and esters of indolepropionic acid directly to the region at which it is desired to induce rootgrowth.

6. The improvement in propagating plants from cuttings and the like which comprises the step of inducing root-growth on the cutting by applying indolepropionic acid directly to the basal end thereof at the region at which it is desired to induce root-growth.

'7. The improvements in propagating plants which comprises the step of inducing root-growth by subjecting the basal end of the cutting to the action of an alkali metal salt of indolepropionic acid.

8. The improvement in propagating plants from cuttings and the like which comprises the step of inducing root-growth by subjecting the basal end of the cutting to the action of a lower alcohol ester of indolepropionic acid.

9. The improvement in propagating plants from cuttings and the like which comprises the step of inducing root-growth by immersion treatment of the basal end of the cutting in an aqueous solution containing indolepropionic acid.

10. The improvement in propagating plants from cuttings and the like which comprises the step of inducing root-growth by immersion treatment of the basal end of the cutting in an aqueous solution containing an alkali metal salt of indolepropionic acid.

PERCY W. ZIMMERMAN. ALBERT E. HITCHCOCK.- 

